In the orthopedic arts, it is known that cartilage tissue in a joint, such as a knee joint, has to be reshaped in order to treat certain joint disorders such as a hyaline cartilage surface irregularities. Generally, arthroscopic surgery is preferred due to the lower rates of morbidity and mortality, and the shorter recovery times experienced by patients. Typically, an orthopedic surgeon will operate arthroscopically on a joint, such as the knee, by inserting one or more trocars into the joint capsule, and then through one of the trocars an arthroscope is inserted so the surgeon can visualize the tissues (i.e., synovium and cartilage) of the joint. The other trocar is used to deploy a surgical instrument, such as a mechanical cutting tool (i.e., a grasper, knife or curette). However, these mechanical cutting tools may damage a significant amount of healthy cartilage while removing damaged or diseased tissue. Because cartilage is avascular and heals slowly, there is a need to develop a tool or device that can remove damaged cartilage tissue while minimizing collateral damage to surrounding healthy cartilage.
The present inventor has considered ablation techniques involving laser technology to address this problem. For the purpose of this disclosure, “ablation” means “the act or process of ablating,” and “ablating means to remove or dissipate by vaporization or melting.” The ablation of cartilage using a 308 nm Excimer laser (a UV laser) in an in vitro cartilage sample is disclosed by J. A. Prodoehl et al. in “308 Excimer Laser Ablation of Cartilage,” Lasers Surg. Med. 15:263-268 (1994). However, Prodoehl's article does not enable one of ordinary skill in the art to perform ablation of cartilage in vivo. Furthermore, the Excimer laser is expensive and relatively bulky so it is not suitable for use in a hospital or outpatient surgery clinical environment. While cheaper lasers that are relatively compact and light are known, such as laser diodes for example, these lasers are not suitable for arthroscopic surgical ablation of cartilage because their wavelength energies are poorly absorbed by cartilage.
Known methods for the ablation of articular cartilage using laser technology employ crystal lasers in the infrared spectrum such as Ho:YAG lasers (wavelength: 2μ) and Er:YAG lasers (wavelength: 2.9μ). However, there are several drawbacks to the application of infrared laser technology to arthroscopic surgery. First, arthroscopic surgery is performed in an aqueous environment. After entering the joint capsule with a trocar, the surgeon infuses an aqueous solution into the joint capsule so that visualization of the joint tissues with an arthroscope is optimized and to prevent excessive deterioration of the joint tissues during the procedure. Unfortunately, the aqueous liquid must be pierced by the infrared laser beam in order to reach the cartilage. In other words, the radiation of the infrared lasers must literally pierce a hole in the water by vaporizing it before reaching the cartilage to be ablated. This means that the infrared laser beam must have considerable energy, which then generates undesirable thermal effects. These undesirable thermal effects increase as the power of the laser increases, which makes quick ablation impossible without damaging a significant amount of healthy joint tissue.
A second drawback of infrared lasers relates to the difficulties encountered when selecting a laser that operates at a wavelength not absorbed well by the aqueous environment. It turns out that a laser that is not absorbed well by the aqueous environment utilized during arthroscopic surgery is also not absorbed well by articular cartilage because of the water content of articular cartilage. Therefore, there is a need to employ some means for enhancing the absorption of laser energy by damaged cartilage tissue that the surgeon wishes to ablate so that energy is preferentially absorbed by the damaged cartilage tissue and not by the healthy hyaline cartilage.
The present inventor has considered the application of an exogenous absorber, such as a dye, to enhance the absorption of laser energy by cartilage tissue to effect selective tissue ablation. However, previous applications of energy absorbing dyes to therapeutic methods have been limited. For example, U.S. Pat. No. 6,221,068 B1 to Fried et al., and incorporated herein by reference for all it discloses, discloses the use of a dye such as Indocyanine Green (ICG) mixed with albumin or fibrinogen to create a tissue “solder.” ICG has an absorption peak at 810 nm when combined with albumin. The tissue solder is applied to opposing edges of a wound, and a commercially available diode laser is used to activate the tissue “solder” and “weld” the tissue edges together. However, U.S. Pat. No. 6,221,068 does not teach, or even suggest, applying the ICG/diode laser combination to effect tissue ablation. On the contrary, U.S. Pat. No. 6,221,068 pertains to using the ICG dye to heat albumin or fibrinogen applied to wound edges to create an adhesive effect. Furthermore, U.S. Pat. No. 6,221,068 does not teach or suggest that the tissue “solder” could be applied to a wound in an aqueous environment.
U.S. Patent Application Publication No. US 2004/0147501 to Dolmans et al. discloses generally “photodynamic therapy,” which pertains to treatment methods employing a photosensitizer to generate reactive radical species to destroy cells in a target tissue. This publication discloses that ICG is a photosensitizer. The photosensitizer is injected into an injection site of a treatment subject and allowed to find its way into the subject's vasculature. After time, the photosensitizer accumulates in a highly vascularized or neovascularized target tissue, such as a rapidly growing tumor. A laser is then used to activate the photosensitizer to generate the radical species used to kill the target tissue. Photodynamic therapy, however, is not an ablation therapy. Furthermore, photodynamic therapy can only be applied to vascularized or neovascularized tissues, which most articular cartilage tissue (e.g., a hyaline cartilage of the knee) is not.
The present invention endeavors to provide an improved method and system for the ablation of cartilage tissue in vivo in a human or animal treatment subject that overcomes the disadvantages of prior art methods and systems. Accordingly, a primary object of the present invention is to overcome the disadvantages of the prior art methods and systems for the ablation of cartilage tissue in vivo in a human or animal treatment subject.
Another object of the present invention is to provide a method and system for the ablation of cartilage tissue that can be employed arthroscopically in an aqueous environment within the joint capsule of a living human or animal treatment subject. Another object of the present invention is to provide a method and system for the ablation of cartilage tissue that employs an economical and compact diode laser so that the method and system may be employed in a hospital and/or outpatient surgical environment.
Yet another object of the present invention is to provide a method and system for the ablation of cartilage that ablates cartilage tissue in a more efficient manner than achieved by prior art methods and systems.